Pressure switch

ABSTRACT

A pressure switch simple to construct, accurate over a very wide range and easily adjustable to provide various combinations of high and low levels comprises a housing, a pressure chamber, a switch blade means movable between contact with first and second movable contact means and a contact stop means having first, second and third camming means controlling respectively the first and second contact means and the switch blade means. The camming means may each be a pair of spaced opposed surfaces in the contact stop means whereby movement of the contact stop means controls the positions of the switch blade means and a movable contact means so that various levels of fluids may be controlled by the pressure switch.

United States Patent Barnes Oct. 9, 1973 PRESSURE SWITCH PrimaryExaminer-Robert K. Schaefer 75 lnventor: Gene A. Barnes, Skokie, n1.Examiner-Wham Attorney-Carlton Hlll et al. [73] Assignee: EatonCorporation, Cleveland, Ohio [22] Filed: Jan. 18, 1972 [57] ABSTRACT[2l] Appl. No.: 218,718 A pressure switch simple to construct, accurateover a very wide range and easily adjustable to provide vari- 52 us. c1.200/83 SA 200/83 WM of high and lfivels mprises a 51 Int. Cl. Hlh 1/48housmg a pressure a swtch blade means 58 Field of Search 200/83 WM 83 smovable between first secmd "9" 200/83 SA 81 4 81 337/311 323 ablecontact means and a contact stop means having first, second and thirdcamming means controlling re- [56] References Cited spectively the firstand second contact means and the switch blade means. The camming meansmay each be UNITED STATES PATENTS a pair of spaced opposed surfaces inthe contact stop 3,450,854 6/1969 Simmons 200/83 WM means wherebymovement of the contact stop means 2930374 3/1960 controls the positionsof the switch blade means and 2 2188.438 l/l940 Judson 200/83 SA movableContact means so that various levels f fluids may be controlled by thepressure switch.

11 Claims, 7 Drawing Figures PRESSURE SWITCH BACKGROUND OF THEINVENTION 1. Field of the Invention This invention generally relates tofluid pressure responsive circuit makers and breakers and moreparticularly concerns a fluid pressure switch having a diaphragm whichis moved by the fluid pressure to actuate a switch blade means movablebetween contact with first and second electrically connected contactmeans. The switch blade and contacts are easily movable by a contactstop means to adjust their position relative to each other so that thepressure necessary to cause actuation thereof may be varied.

2. Prior Art The use of pressure switches to be responsive to functionsof pressure such as controlling the level of fluid in a receptacle isold and well known. It is also known to provide a means forautomatically controlling the level of fluid between an upper and lowerlevel in relationships which are known, as for example, the constantreset level relationship, the constant differential reset levelrelationship, and the proportional reset level relationship.

In what is known as the constant reset level, the relationship of theupper and lower levels is such that the lower level of the fluid orpressure remains constant while the upper level of the fluid or pressureis varied. The constant differential reset level" indicates therelationship wherein the difference between the high and low pressure orfluid levels remains constant so that as the upper level is increased ordecreased, the lower level remains at a predetermined constantdifferential therefrom. With the proportionate reset level" an increaseor decrease in the upper fluid or pressure level causes a proportionateincrease or decrease in the lower fluid or pressure level so that, forexample, as the upper level increases, the difference between it and thelower level increases proportionately.

According to the prior art these various pressure or level relationshipsmay not be produced by a single basic pressure switch structure, butrather require extensive modifications of a basic assembly to producewhat in effect are separate switch structures. Moreover, with the priorart constructions, it is not possible to provide a combination of thesedifferent level rela tionships in a single pressure switch structure.

A particularly advantageous use of the invention herein occurs inautomatic clothes washing machines wherein it is desirable that a widerange of fluid levels be easily and accurately maintained by as small,as economical and as fool-proof a switch structure as is possible. Inrecent years these machines have increased in size and hence it isbecoming more important that the water level in the machines becontrollable over a wider range of enable these higher capacity machinesto carry a wide range of loads. Thus, for example, it is no longerunusual for the water level selections to vary from four inches for alight load to 18 or more inches for a heavy load. Compounding theserequirements is a greater emphasis on a higher degree of accuracy,stability, consistency of performance, and a desire for a smaller sizepressure switch. Moreover, the higher motor requirement have increasedthe electrical load thereby increasing the effects of contact chatter,contact bounce and subsequent contact welding.

The above noted deficiencies in the prior art are by way of example andare only representative of problems being encountered in the developmentof pressure responsive switch means which can meet the requirements oftodays rapidly expanding technology.

SUMMARY OF THE INVENTION The many problems of the prior art are overcomeby the pressure responsive switch means according to the inventionherein in which an easily positionable contact stop means cooperateswith a switch blade means movable between contact with a first andsecond contact means to move the switch blade means and the first andsecond contact means relative to one another and to limit their extentof movement so that the amount of pressure and hence the fluid level towhich the switch means will be responsive to may be simply andaccurately varied. The switch means further includes a pressure chamberbounded in part by a diaphragm means with the pressure chamber beingadapted to be connected to a variable pressure source. The switch blademeans is operatively connected to the diaphragm means and the switchblade means has connected therewith a variable biasing means to vary theforce required to move the switch blade means whereby the switch blademeans may be movable against the force of the biasing means from thefirst contact means to the second contact means.

The first, second and third camming means are each a pair of spacedopposed surfaces receiving therebetween a portion of the first contactmeans, the second contact means and a switch blade means, respectively,so that movement of the cam stop means controls the position of theswitch blade means and the movable contact means. The opposed surfacesof the camming means are each spaced apart a distance to allow movementof the portion of the respective contact means and switch blade meansreceived therein within predetermined limits. The first and secondcontact means may be biased toward each other and toward intermediateswitch blade means and will lie adjacent the innersurface of the firstand second camming means re spectivley so that it may move between theopposed camming surfaces in response to contact by the switch blademeans whereby the rapid movement of the switch blade means may bebrought to a stop with the contact means against the outer cammingsurface and in abutment with the switch blade means. The controlledmovement of the contact means between the inner and outer surfaces ofits respective cam means greatly reduces any tendency for the contactsto bounce or chatter. By varying the angle of the arm of the contactmeans with respect to the switch blade means, any amount of wiping ofthe contacts can be obtained. The

control of amount of wiping of the contacts is impor- I tant in that itallows the generation of a force multiplication which will break anycontact welds which may have been formed between the contacts.

To produce a constant differential reset level relationship between theupper and lower fluid levels the opposed surfaces of the first andsecond camming means are arranged generally parallel to each other sothat the difference between the high and low pressure of fluid levelsremains constant. To produce a constant reset level relationship theopposed surfaces of the second camming means are arranged so that uponmovement of the contact stop means the second contact means remainsgenerally in its original position whereas the first camming meansdiverges therefrom as required to produce a predetermined upper level.With the proportionate reset level the first and second camming meansare divergent in a proportional relationship to the movement of thecontact stop so that, for example, as the upper level increases, thedifference between it and the lower level increases proportionately. Inaddition to being able to control these basic relationships it may beseen that the first, second an third camming means may be varied toproduce practically all relationships or combinations thereof. Moreover,it will be understood by those skilled in the art that the pressureswitch housing according to the invention herein may be quickly snappedopen and a new and/or different contact stop means readily inserted toallow this very wide range of operation.

The unique features of the pressure responsive switch according to theinvention may be seen in the fact that the switch speed is a function ofdiaphragm speed which will cause the switch making to be bounced freedue to a slow speed. Also, the arc generation due to breaking contactsis minimized by being able to control the speed of opening of thecontacts whereas a conventional switch will break at a great enoughspeed to cause high are generation. The camming means on the contactstop means provide positive stops for the contact means as well as theswitch blade means for each of an almost infinite variety of positions.This thereby allows ready control of the diaphragm stroke and the curvein a graph of force on the switch blade means versus stroke of theswitch blade means is greatly improved by being able to select just theportion of the curve required for each situation. Furthermore, thesestops provided by the camming means drastically improve the ease ofanalysis and design of the switch to meet a desired condition. Stillfurther the fact that all of the forces are directly transmitted throughthe contact points produces very high contact forces and hence allowsgreater electrical power and avoids chatter and other problemsassociated with the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantagesof the invention will be readily apparent from the following descriptionof certain preferred embodiments thereof, taken in conjunction with theaccompanying drawings although variations and modifications may beeffected without departing from the spirit and scope of the novelconcepts of the disclosure and in which:

FIG. 1 is a schematic cross sectional diagram of the invention asembodied in a typical washing machine water system;

FIG. 2 is a schematic cross sectional elevation of an embodiment in apressure responsive switch means adapted to be used in the system ofFIG. 1;

FIG. 3 is an isolated view of the contact stop means of FIG. 2 with theswitch blade means shown in the normally opened position as opposed tothe normally closed position of FIG. 2;

FIG. 4 is an isolated view of another embodiment of a contact stop meansconfigured to provide a generally constant differential reset levelrelationship;

FIG. 5 is a graph of force versus stroke of the switch blade meansindicating the ability to select a desired portion of the curve betweenupper and lower levels;

FIG. 6 is a graph of water level versus adjustment and indicates theability of the pressure responsive switch means of the invention toprovide various fluid level relationships;

FIG. 7 is another graph of water level or pressure versus adjustmentwhich serves to indicate the examples of the combinations of fluid levelrelationships which may be obtained with the invention herein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the schematicdiagram of a typical wash machine water system in FIG. 1 there may beseen a pressure responsive switch means 10 according to the inventionhaving an inlet 12 in communication with a pressure conduit 14 which inturn is in pressure communication with a wash machine tube 20. Apressurized water supply schematically represented by the conduit 22 isopened and closed by a solenoid water valve 24 which in turn isconnected by suitable electrical connection means 26 to the pressureswitch 10 whereby the solenoid water valve is controlled by the pressureswitch 10. When the water valve 24 is opened water runs into the tub 20through the conduit 23 to fill the tub to a desired water level. The tub20 may include the conventional drain means 30 and pump 32 for drainingthe wash water.

The depth of water or range of levels of water in the tub 20 isindicated by the arrow 36 extending between the bottom of the tub 20 andthe desired upper water level 37. It is important in a wash machine tocontrol the level of water. at two points, the first is the desiredwater level 37 at which point the water is cycled or tripped off afterfilling the tub 20 and the second point is the lower water level limitindicated at 38 at which point the switch is reset and the water iscycled on. By means of the invention herein both the desired upper waterlevel 37 and the lower water limit 38 may be easily and convenientlyregulated to have the relationships of levels 37 and 38 known asconstant differential, a proportional differential or constant reset. Itis also unique to this invention that variations of these combinationsmay be possible. These relationships will be explained in greater detailwith regard to the operation of the invention.

With the demands for washing machines having increased capacity, it hasbecome more important to be able to control the water level 36 in thetub 20 over a wider range since a machine of high capacity must still beable to handle a minimum load. For example, variations in the waterlevel 36 from 4 inches for a light load to eighteen or more inches for aheavy load are no longer unusual. In addition to this requirement agreater emphasis is being placed on the accuracy and consistency of thewater levels. Compounding these requirements is the desire for apressure switch of minimum size which may be easily accommodated in themachine cabinet.

All of the above noted requirements and more are met by the pressureresponsive switch means 10 of the invention.

Referring to FIG. 2 there is shown an enlarged cross sectional view ofthe pressure switch 10 embodying the instant invention. Essentially thepressure switch 10 comprises an expandable air chamber 15 communicatingat one portion thereof with the conduit 14 and h aving a diaphragm means16 bounding another portion thereof. A diaphragm means 16 is connectedby a translation member 17 to an elongated blade-like switch plate means40 so that movements of the diaphragm 16 in response to pressure changesin the pressure chamber 15 are transferred to the switch blade means 40by the translation member 17. A first contact means 50 is positioned onone side at an angle to the switch blade means 40. The first contactmeans 50 includes a contact 52. A second contact means is situated on anopposite side of the switch blade means 40 and also extends at an anglethereto. The second contact means includes a contact 62. Both thecontact means 50 and 60 may comprise flexible, elongated blade members.The contact means 50, the contact means 60 and the switch blade means 40each have portions engaging respectively a first camming means 55, asecond camming means 65 and a third camming means 45 which camming meansare located on a contact stop means 70 and control the permissiblemovement of the respective contact means and switch blade. As shown, thecontact stop means 70 may be rotatably mounted in a housing 11 of thepressure switch means 10.

A tension spring 80 has a first end 81 attached to the switch blademeans 40 and a second end 82 attached to an adjustment means 85 wherebythe tension in the spring means 80 may be varied. The resilient tensionforce in the spring 80 acts against the force transmitted through thetranslation member 17 by an increasing pressure in the pressure chamber15. Thus, the increasing force on a diaphragm 16 as transmitted by thetranslation means 17 is opposed by the tension means 80 until the forceon the translation member 17 overcomes the tension force on the springmeans 80 at which point the switch blade means 40 is moved from itsnormally closed position as shown in FIG. 2 to a normally openedposition as illustrated in FIG. 3. Each of the means 40, 50 and 60includes electrically conductive means so that the switching of theswitch blade 40 between the first contact means 50 and the secondcontact means 60 breaks one circuit and makes another in response to thechange in pressure in the pressure chamber 15. It will be understoodthat generally, the pressure switch means acts as a transducer,converting a hydropneumatic function into an electrical function. Thatis, the increase in the level 36 of water in the tub 20 as shown in FIG.1, causes a column of water to rise in the conduit 14 compressing theair in the upper end thereof, which air acts on a pressure chamberdiaphragm 16 and the pressure switch 10 to move the diaphragm 16 inrelation to the pressure and thereby open and close electrical circuitsof which the switch blade means 40 and the first and second contactmeans 50, 60, form a part of. As the water depth 36 reaches a waterlevel 37 determined primarily by the position of the first camming means55 and the third camming means 45 on the contact stop means 70, an airpressure head in the chamber causes the diaphragm means 16 to overcome apredetermined tension in the spring means 80 to thereby move the contactarm 40 from the normally closed contact 50 which is part of a circuitthat will activate the solenoid 24 to allow water under pressure in thepipe 22 to be dispensed into the tub through the inlet 23 and move it tothe normally closed contact means 60 thereby stopping further flow ofwater into the tub 20 and to activate the circuit of which contact means60 may be a part. As the water level decreases and the consequentpressure in the chamber 15 decreases the diaphragm 16 will be moved in adirection whereby the contact between the switch blade 40 and the secondcontact means is broken and the contact between the switch blade means40 and the contact means 50 is made to thereby activate the solenoid 24and again increase the water level in the tub 20 to the desired selectedlevel 37 at which point the cycle is repeated.

The first, second and third camming means 55, and 45, respectively, eachcomprise a pair of opposed inner and outer surfaces 56, 57; 66, 67; and46, and 47. Each of the respective camming means 55, 65 and 45 receivebetween their respective inner and outer surfaces a portion of therespective first camming means 50a, the second camming means 60a and theswitch blade means 400. With such arrangement the movement of the camstop means controls the relative positions of the switch blade means 50,60 and the movable contact means 40. The opposed surfaces of the cammingmeans are each spaced apart a distance to allow movement of the portionof their respective contact means and switch blade means receivedtherein within predetermined limits. As shown in FIGS. 2, 3 and 4 thecontact stop means may take the form of a generally cylindrically shapedrotatable member wherein the first camming means takes the form of agroove means on the outer surface of the generally cylindrically shapedmember and receives the portion 50 a of the first contact means therein.Similarly, the second camming means 65 will be a groove on the outergenerally cylindrically shaped surface of the contact stop means 70 andreceives a portion 60a of the second movable contact means therein. Thethird camming means 45 also is a groove means on a generallycylindrically shaped surface of the contact stop means 70 and receives aportion 40a of the switch blade means therein. Accordingly, it may beseen that as the contact stop means 70 is rotated by means of a portion70a projecting beyond the housing 11, the position of the first contactmeans 50 will vary in relation to the generally constant position of thesecond contact means 60. This variation in the location of the firstcontact means 50 has the effect of changing the position of the switchblade means 40 when it is in its normally closed position so that theforces acting on the switch blade means 40 in opposition to the forcesacting through the translation member 17 will be varied and hence thetrip or upper level position 37 of the fluid will be varied. Suitablegauge and/or indicator means in conjunction with the contact stop means70 may be provided to allow selection of the desired water level inaccordance with common and well known expressions. In the embodimentshown the lands 70b and 700 between the camming means 55, 45 and 65 maybe of a width or configuration in accordance with efficient operationand the sizes of the contacts 52, 42, and 62, respectively.

The first contact means 50 and the second contact means 60 may be biasedby means not shown toward each other and toward the intermediate switchblade means 40 to bear against the outer camming surface 57 and theinner camming surface 66 respectively, when they are free from contactwith the switch blade means 40. Accordingly, as the switch blade means40 snaps into contact with the first contact means 50 it moves thecontact means against its inward biasing force and moves the portion 50ainto contact with the inner camming surface 56 of the first cammingmeans 55. When the pressure force in the chamber becomes great enough tomove the switch blade means 40 and break contact with the first contactmeans 50 the portion 50a of the first contact means 50 returns to itsoriginal position biased against the outer camming surface 57. At thesecond contact means 60 the switch blade means 40 moves the portion 60afrom its position biased against the inner camming surface 66 to aposition where it contacts the outer camming surface 67 as is moreclearly shown in FIG. 3. The inward bias of the contact means 50 and 60has the effect of decelerating the switch blade means 40 at the end ofits snap-type action movement and also accelerating the movement of theswitch blade means 40 at the beginning of its movement. This has theeffect of reducing if not eliminating the amount of, bounce of thecontacts and also minimizes chatter. Forces between the members 40, 50and 60 are transmitted through the contact points 42, 52 and 62 so thatan excellent contact results with accordant improvement of chatter,capacity and general functioning. The angular relationship of thecontact means 50 and 60 to the switch blade 40 and their differentrelative arcuate movement together produces a wiping of the contacts 42,52 and 62. This wiping is important in that it allows the generation ofa force multiplication which will break any contact welds that may havebeen formed between the contacts while they were together. This isparticularly important with the demands for higher electrical capacityof these switches. It is another significant feature of this inventionthat the angular relationship of the contact means 50 and 60 with theswitch blade means 40 may be varied to vary the amount of wiping of thecontacts. By this means the wiping may be reduced to zero and thefriction present in the mechanism due to the wiping of the contacts mayin theory be eliminated.

The translation member 17 may be a resilient springlike member whichwill act to store energy during initial movement of the diaphragm 16 andprior to the diaphragm force overcoming the resilient spring means 80 sothat after the force of the spring means 80 has been overcome thetranslation member 17 will tend to release its energy and effectivelysnap the switch blade means 40 between the contact means 50 and 60. Itwill be understood by those skilled in the art that the resilience ofthe translation member 17 relative to the spring means 80 and the forceon the diaphragm 16 may be designed to vary the movement characteristicsof the switch blade 40. Thus, the translation member 17 may vary frombeing very stiff to being very flexible depending upon the switchingcharacteristics desired. The ease of modification by changing this onepart is yet another example of the flexibility and adaptability of theswitch means of the invention.

By means of the described invention fluid levels may be simply andaccurately varied. A further illustration of the range of variationswhich may be effected is the contact stop means 170 in FIG. 4. Here thefirst contact means 50 is received in a first camming means 155, thesecond contact means 60 is received in a second camming means 165 andthe switch blade means 40 is received in a third camming means 145. Inthis case, however, the camming surfaces 156, 157 of the first cammingmeans 155 and the camming surface 166 and 167 of the second cammingmeans 165 are parallel to each other to produce what is known as theconstant differential level wherein the difference between the upper andlower levels remains constant as they are varied. Other contact stopsmay be designed to produce all fluid level relationships which can beforeseen. Further, the variation and flexibility is readily effected.For example, by means of lateral protrusions 172 in the third cammingmeans 45 and 145 respectively, the switch blade means may be manuallyurged against the normally closed first contact means to therebyoverride the automatic pressure responsiveness. Clearly, other anddifferent variations will be apparent to those skilled in the art havingknowledge of my invention.

Referring to FIG. 5 there may be seen a graph of force transmitted tothe switch blade member 40 by the translation member 17 versus thedisplacement of the switch blade means 40 to illustrate the ability ofthe invention herein to allow selection of a particular portion of anormal toggle curve. Thus, the normal toggle curve is illustrated at 90,the upper level or trip line is indicated at 92, and the reset or lowerlevel is indicated at 94. The line indicates that the pressure willbuild up on the switch blade means 40 at the normally closed stop untilthe trip point 96 at the trip level 92 is reached at which point theswitch blade will move and the force will decrease until the normallyopened contact means 60, in FIG. 2 is reached. At this point the forcewill again increase as indicated by the line 97. Effectively the lines95 and 97 indicate the limits of movement of the switch blade means 40and hence allow selection of any portion of the curve 90 as representedby the portion 98. Moreover, the selection may be simply and accuratelyeffected.

Referring to FIG. 6 there may be seen a graph of the water level versusadjustemnt of the contact stop means which will allow the variousrelationships of the upper and lower levels. For example, the constantreset level relationship is illustrated by the lines 100 and 103; theconstant differential reset level is illustrated by the lines 102 and103; and the proportionate reset level relationship is illustrated bythe lines 101 and 103. In each case the line 103 represents the trip orupper level and lines 100, 101 and 102 represent the reset or lowerlevel.

In FIG. 7 another example of possible variations in the trip and resetlevels are illustrated by the lines 1 10 through 117. In this case lines110, 111 illustrate one alternate trip level configuration whereas line112'represents an alternate trip level. Similarly, lines 113 through 117 represent individual alternate variations of relationships. From theforegoing description of the invention it may be seen that the manyproblems of the prior art are overcome by the pressure responsive switchmeans 10 according to the invention herein.

Although minor modifications might be suggested by those versed in theart, it should be understood that I wish to embody within the scope ofthe patent warranted hereon all such modifications as reasonably andproperly come within the scope of my contribution to the art.

I claim:

1. In an electrical switch means having a switch blade means movablebetween electrical contact with a first and second movable contactmeans, the improvement comprising a contact stop means including a firstcamming means controlling said first movable contact means, a secondcamming means controlling said second movable contact means, a thirdcamming means controlling the position of said switch blade meansrelative to said first and second movable contact means, said cammingmeans being coaxial, and a common actuator therefor to effect avariation in the point of contact between said switch blade meansrelative to said first and second movable contact means.

2. A switch means according to claim 1 wherein said first, second andthird camming means are each a pair of spaced, opposed annular surfaceson said contact stop means whereby movement of said cam stop meanscontrols the position of said switch blade means and said movablecontact means.

3. A switch means according to claim 2 wherein said opposed surfaces ofsaid first camming means receive a portion of said first contact meanstherein, said opposed surfaces of said second camming means receiving aportion of said second movable contact means therein, said opposedsurfaces of said third camming means receiving a portion of said switchblade means therein, said opposed surfaces of said camming means eachbeing spaced apart a distance to allow movement of the portion of therespective contact means and switch blade means received therein withinpredetermined limits.

4. A switch means according to claim 3 wherein said opposed surfaces ofsaid first and second camming means are generally parallel to each otherwhereby a constant differential reset level relationship is produced.

5. A switch means according to claim 1 wherein said switch blade meansis connected with a pressure responsive means whereby pressure changesmay cause movement of said switch blade means in generally oppositefirst and second directions, a resilient biasing means connected withsaid switch blade means to oppose movement of said switch blade means bysaid pressure responsive means in said first direction and to assistmovement of said switch blade means in said second direction.

6. A switch means according to claim 5 wherein the force exerted by saidresilient biasing means may be adjusted to vary the amount of pressurenecessary to cause movement of said pressure responsive means.

7. A switch means according to claim 5 wherein said pressure responsivemeans is a diaphragm which bounds a pressure chamber, said pressurechamber being adapted to be operatively connected to a variable pressuresource, said diaphragm being a polyurethane film.

8. A switch means according to claim 3 wherein said opposed surfaces ofsaid camming means are spaced apart a distance to allow movement of saidfirst and second contact means, said first and second contact meansbeing biased toward said switch blade means, said contacts between saidswitch blade and said contact means being arranged so that said switchblade means overcomes the bias of the contact means it is engaging andmoves said contact means from one opposite surface of its respective cammeans to the other opposite surface.

9. A switch means according to claim 1 wherein the contact means and theswitch blade means are positioned relative to each other at an effectiveangle of inclination, said effective angles of inclination beingvariable by said camming means on said contact stop means whereby theamount of wipe of the contacts may be varied.

10. A switch means according to claim 1 wherein said first and secondmovable contact means and said switch blade means each have protrudingcontact points thereon, said contact points providing the points ofengagement of the switch blade means with the respective contact meanswhereby the opposing forces in the switch blade means and in the contactmeans are transmitted directly through the contact points.

11. In an electrical switch means having switch blade means movablebetween electrical contact with a first and second movable contactmeans, the improvement comprising a contact stop means in the form of agenerally cylindrical rotatable member, having a first camming meansextending thereabout controlling said first movable contact means, asecond camming means spaced from said first camming means forcontrolling said second movable contact means, and a third camming meanscontrolling the position of said switch blade means relative to saidfirst and second movable contact means, said first, second and thirdcamming means each comprising a pair of spaced opposed camming surfacesextending about said cylindrical shaped rotatable member andformingfirst, second and third camming grooves, said first groove receiving aportion of said first contact means therein, said second groovereceiving a portion of said second movable contact means therein, andsaid third groove receiving a portion of said switch blade meanstherein, for varying the positions of said movable contact means andsaid switch blade means relative to each other upon turning movement ofsaid cylindrical member.

1. In an electrical switch means having a switch blade means movablebetween electrical contact with a first and second movable contactmeans, the improvement comprising a contact stop means including a firstcamming means controlling said first movable contact means, a secondcamming means controlling said second movable contact means, a thirdcamming means controlling the position of said switch blade meansrelative to said first and second movable contact means, said cammingmeans being coaxial, and a common actuator therefor to effect avariation in the point of contact between said switch blade meansrelative to said first and second movable contact means.
 2. A switchmeans according to claim 1 wherein said first, second and third cammingmeans are each a pair of spaced, opposed annular surfaces on saidcontact stop means whereby movement of said cam stop means controls theposition of said switch blade means and said movable contact means.
 3. Aswitch means according to claim 2 wherein said opposed surfaces of saidfirst camming means receive a portion of said first contact meanstherein, said opposed surfaces of said second camming means receiving aportion of said second movable contact means therein, said opposedsurfaces of said third camming means receiving a portion of said switchblade means therein, said opposed surfaces of said camming means eachbeing spaced apart a distance to allow movement of the portion of therespective contact means and switch blade means received therein withinpredetermined limits.
 4. A switch means according to claim 3 whereinsaid opposed surfaces of said first and second camming means aregenerally parallel to each other whereby a constant differential resetlevel relationship is produced.
 5. A switch means according to claim 1wherein said switch blade means is connected with a pressure responsivemeans whereby pressure changes may cause movement of said switch blademeans in generally opposite first and second directions, a resilientbiasing means connected with said switch blade means to oppose movementof said switch blade means by said pressure responsive means in saidfirst direction and to assist movement of said switch blade means insaid second direction.
 6. A switch means according to claim 5 whereinthe force exerted by said resilient biasing means may be adjusted tovary the amount of pressure necessary to cause movement of said pressureresponsive means.
 7. A switch means according to claim 5 wherein saidpressure responsive means is a diaphragm which bounds a pressurechamber, said pressure chamber being adapted to be operatively connectedto a variable pressure source, said diaphragm being a polyurethane film.8. A switch means according to claim 3 wherein said opposed surfaces ofsaid camming means are spaced apart a distance to allow movement of saidfirst and second contact means, said first and second contact meansbeing biased toward said switch blade means, said contacts between saidswitch blade and said contact means being arranged so that said switchblade means overcomes the bias of the contact means it is engaging andmoves said contact means from one opposite surface of its respective cammeans to the other opposite surface.
 9. A switch means according toclaim 1 wherein the contact means and the switch blade means arepositioned relative to each other at an effective angle of inclination,said effective angles of inclination being variable by said cammingmeans on said contact stop means whereby the amount of wipe of thecontacts may be vaRied.
 10. A switch means according to claim 1 whereinsaid first and second movable contact means and said switch blade meanseach have protruding contact points thereon, said contact pointsproviding the points of engagement of the switch blade means with therespective contact means whereby the opposing forces in the switch blademeans and in the contact means are transmitted directly through thecontact points.
 11. In an electrical switch means having switch blademeans movable between electrical contact with a first and second movablecontact means, the improvement comprising a contact stop means in theform of a generally cylindrical rotatable member, having a first cammingmeans extending thereabout controlling said first movable contact means,a second camming means spaced from said first camming means forcontrolling said second movable contact means, and a third camming meanscontrolling the position of said switch blade means relative to saidfirst and second movable contact means, said first, second and thirdcamming means each comprising a pair of spaced opposed camming surfacesextending about said cylindrical shaped rotatable member and formingfirst, second and third camming grooves, said first groove receiving aportion of said first contact means therein, said second groovereceiving a portion of said second movable contact means therein, andsaid third groove receiving a portion of said switch blade meanstherein, for varying the positions of said movable contact means andsaid switch blade means relative to each other upon turning movement ofsaid cylindrical member.